Class StringBuffer

A thread-safe, mutable sequence of characters.
A string buffer is like a String, but can be modified. At any
point in time it contains some particular sequence of characters, but
the length and content of the sequence can be changed through certain
method calls.

String buffers are safe for use by multiple threads. The methods
are synchronized where necessary so that all the operations on any
particular instance behave as if they occur in some serial order
that is consistent with the order of the method calls made by each of
the individual threads involved.

The principal operations on a StringBuffer are the
append and insert methods, which are
overloaded so as to accept data of any type. Each effectively
converts a given datum to a string and then appends or inserts the
characters of that string to the string buffer. The
append method always adds these characters at the end
of the buffer; the insert method adds the characters at
a specified point.

For example, if z refers to a string buffer object
whose current contents are "start", then
the method call z.append("le") would cause the string
buffer to contain "startle", whereas
z.insert(4, "le") would alter the string buffer to
contain "starlet".

In general, if sb refers to an instance of a StringBuffer,
then sb.append(x) has the same effect as
sb.insert(sb.length(), x).

Whenever an operation occurs involving a source sequence (such as
appending or inserting from a source sequence) this class synchronizes
only on the string buffer performing the operation, not on the source.

Every string buffer has a capacity. As long as the length of the
character sequence contained in the string buffer does not exceed
the capacity, it is not necessary to allocate a new internal
buffer array. If the internal buffer overflows, it is
automatically made larger.
As of release JDK 5, this class has been supplemented with an equivalent
class designed for use by a single thread, StringBuilder. The
StringBuilder class should generally be used in preference to
this one, as it supports all of the same operations but it is faster, as
it performs no synchronization.

Method Detail

length

the length of the sequence of characters currently
represented by this object

capacity

public int capacity()

Returns the current capacity. The capacity is the amount of storage
available for newly inserted characters, beyond which an allocation
will occur.

Returns:

the current capacity

ensureCapacity

public void ensureCapacity(int minimumCapacity)

Ensures that the capacity is at least equal to the specified minimum.
If the current capacity is less than the argument, then a new internal
array is allocated with greater capacity. The new capacity is the
larger of:

The minimumCapacity argument.

Twice the old capacity, plus 2.

If the minimumCapacity argument is nonpositive, this
method takes no action and simply returns.

Parameters:

minimumCapacity - the minimum desired capacity.

trimToSize

public void trimToSize()

Attempts to reduce storage used for the character sequence.
If the buffer is larger than necessary to hold its current sequence of
characters, then it may be resized to become more space efficient.
Calling this method may, but is not required to, affect the value
returned by a subsequent call to the capacity() method.

Since:

1.5

setLength

public void setLength(int newLength)

Sets the length of the character sequence.
The sequence is changed to a new character sequence
whose length is specified by the argument. For every nonnegative
index k less than newLength, the character at
index k in the new character sequence is the same as the
character at index k in the old sequence if k is less
than the length of the old character sequence; otherwise, it is the
null character '\u0000'.
In other words, if the newLength argument is less than
the current length, the length is changed to the specified length.

If the newLength argument is greater than or equal
to the current length, sufficient null characters
('\u0000') are appended so that
length becomes the newLength argument.

codePointAt

public int codePointAt(int index)

Returns the character (Unicode code point) at the specified
index. The index refers to char values
(Unicode code units) and ranges from 0 to
length() - 1.

If the char value specified at the given index
is in the high-surrogate range, the following index is less
than the length of this sequence, and the
char value at the following index is in the
low-surrogate range, then the supplementary code point
corresponding to this surrogate pair is returned. Otherwise,
the char value at the given index is returned.

Parameters:

index - the index to the char values

Returns:

the code point value of the character at the
index

Since:

1.5

codePointBefore

public int codePointBefore(int index)

Returns the character (Unicode code point) before the specified
index. The index refers to char values
(Unicode code units) and ranges from 1 to length().

If the char value at (index - 1)
is in the low-surrogate range, (index - 2) is not
negative, and the char value at (index -
2) is in the high-surrogate range, then the
supplementary code point value of the surrogate pair is
returned. If the char value at index -
1 is an unpaired low-surrogate or a high-surrogate, the
surrogate value is returned.

Parameters:

index - the index following the code point that should be returned

Returns:

the Unicode code point value before the given index.

Since:

1.5

codePointCount

public int codePointCount(int beginIndex,
int endIndex)

Returns the number of Unicode code points in the specified text
range of this sequence. The text range begins at the specified
beginIndex and extends to the char at
index endIndex - 1. Thus the length (in
chars) of the text range is
endIndex-beginIndex. Unpaired surrogates within
this sequence count as one code point each.

Parameters:

beginIndex - the index to the first char of
the text range.

endIndex - the index after the last char of
the text range.

Returns:

the number of Unicode code points in the specified text
range

Since:

1.5

offsetByCodePoints

public int offsetByCodePoints(int index,
int codePointOffset)

Returns the index within this sequence that is offset from the
given index by codePointOffset code
points. Unpaired surrogates within the text range given by
index and codePointOffset count as
one code point each.

Parameters:

index - the index to be offset

codePointOffset - the offset in code points

Returns:

the index within this sequence

Since:

1.5

getChars

Characters are copied from this sequence into the
destination character array dst. The first character to
be copied is at index srcBegin; the last character to
be copied is at index srcEnd-1. The total number of
characters to be copied is srcEnd-srcBegin. The
characters are copied into the subarray of dst starting
at index dstBegin and ending at index:

setCharAt

public void setCharAt(int index,
char ch)

The character at the specified index is set to ch. This
sequence is altered to represent a new character sequence that is
identical to the old character sequence, except that it contains the
character ch at position index.

The index argument must be greater than or equal to
0, and less than the length of this sequence.

append

The characters of the String argument are appended, in
order, increasing the length of this sequence by the length of the
argument. If str is null, then the four
characters "null" are appended.

Let n be the length of this character sequence just prior to
execution of the append method. Then the character at
index k in the new character sequence is equal to the character
at index k in the old character sequence, if k is less
than n; otherwise, it is equal to the character at index
k-n in the argument str.

Parameters:

str - a string.

Returns:

a reference to this object.

append

The characters of the StringBuffer argument are appended,
in order, to the contents of this StringBuffer, increasing the
length of this StringBuffer by the length of the argument.
If sb is null, then the four characters
"null" are appended to this StringBuffer.

Let n be the length of the old character sequence, the one
contained in the StringBuffer just prior to execution of the
append method. Then the character at index k in
the new character sequence is equal to the character at index k
in the old character sequence, if k is less than n;
otherwise, it is equal to the character at index k-n in the
argument sb.

This method synchronizes on this (the destination)
object but does not synchronize on the source (sb).

append

Characters of the argument s, starting at
index start, are appended, in order, to the contents of
this sequence up to the (exclusive) index end. The length
of this sequence is increased by the value of end - start.

Let n be the length of this character sequence just prior to
execution of the append method. Then the character at
index k in this character sequence becomes equal to the
character at index k in this sequence, if k is less than
n; otherwise, it is equal to the character at index
k+start-n in the argument s.

If s is null, then this method appends
characters as if the s parameter was a sequence containing the four
characters "null".

append

Appends the string representation of a subarray of the
char array argument to this sequence.

Characters of the char array str, starting at
index offset, are appended, in order, to the contents
of this sequence. The length of this sequence increases
by the value of len.

The overall effect is exactly as if the arguments were converted
to a string by the method String.valueOf(char[],int,int),
and the characters of that string were then
appended to this character sequence.

delete

Removes the characters in a substring of this sequence.
The substring begins at the specified start and extends to
the character at index end - 1 or to the end of the
sequence if no such character exists. If
start is equal to end, no changes are made.

deleteCharAt

Removes the char at the specified position in this
sequence. This sequence is shortened by one char.

Note: If the character at the given index is a supplementary
character, this method does not remove the entire character. If
correct handling of supplementary characters is required,
determine the number of chars to remove by calling
Character.charCount(thisSequence.codePointAt(index)),
where thisSequence is this sequence.

replace

Replaces the characters in a substring of this sequence
with characters in the specified String. The substring
begins at the specified start and extends to the character
at index end - 1 or to the end of the
sequence if no such character exists. First the
characters in the substring are removed and then the specified
String is inserted at start. (This
sequence will be lengthened to accommodate the
specified String if necessary.)

insert

Inserts the string representation of a subarray of the str
array argument into this sequence. The subarray begins at the
specified offset and extends lenchars.
The characters of the subarray are inserted into this sequence at
the position indicated by index. The length of this
sequence increases by lenchars.

Parameters:

index - position at which to insert subarray.

str - A char array.

offset - the index of the first char in subarray to
be inserted.

len - the number of chars in the subarray to
be inserted.

Returns:

This object

Throws:

StringIndexOutOfBoundsException - if index
is negative or greater than length(), or
offset or len are negative, or
(offset+len) is greater than
str.length.

Since:

1.2

insert

Inserts the string representation of the Object
argument into this character sequence.

The overall effect is exactly as if the second argument were
converted to a string by the method String.valueOf(Object),
and the characters of that string were then
inserted into this character
sequence at the indicated offset.

The offset argument must be greater than or equal to
0, and less than or equal to the length
of this sequence.

insert

The characters of the String argument are inserted, in
order, into this sequence at the indicated offset, moving up any
characters originally above that position and increasing the length
of this sequence by the length of the argument. If
str is null, then the four characters
"null" are inserted into this sequence.

The character at index k in the new character sequence is
equal to:

the character at index k in the old character sequence, if
k is less than offset

the character at index k-offset in the
argument str, if k is not less than
offset but is less than offset+str.length()

the character at index k-str.length() in the
old character sequence, if k is not less than
offset+str.length()

The offset argument must be greater than or equal to
0, and less than or equal to the length
of this sequence.

insert

Inserts the string representation of the char array
argument into this sequence.

The characters of the array argument are inserted into the
contents of this sequence at the position indicated by
offset. The length of this sequence increases by
the length of the argument.

The overall effect is exactly as if the second argument were
converted to a string by the method String.valueOf(char[]),
and the characters of that string were then
inserted into this character
sequence at the indicated offset.

The offset argument must be greater than or equal to
0, and less than or equal to the length
of this sequence.

insert

The characters of the CharSequence argument are inserted,
in order, into this sequence at the indicated offset, moving up
any characters originally above that position and increasing the length
of this sequence by the length of the argument s.

The result of this method is exactly the same as if it were an
invocation of this object's
insert(dstOffset, s, 0, s.length())
method.

If s is null, then the four characters
"null" are inserted into this sequence.

insert

Inserts a subsequence of the specified CharSequence into
this sequence.

The subsequence of the argument s specified by
start and end are inserted,
in order, into this sequence at the specified destination offset, moving
up any characters originally above that position. The length of this
sequence is increased by end - start.

The character at index k in this sequence becomes equal to:

the character at index k in this sequence, if
k is less than dstOffset

the character at index k+start-dstOffset in
the argument s, if k is greater than or equal to
dstOffset but is less than dstOffset+end-start

the character at index k-(end-start) in this
sequence, if k is greater than or equal to
dstOffset+end-start

The dstOffset argument must be greater than or equal to
0, and less than or equal to the length
of this sequence.

The start argument must be nonnegative, and not greater than
end.

The end argument must be greater than or equal to
start, and less than or equal to the length of s.

If s is null, then this method inserts
characters as if the s parameter was a sequence containing the four
characters "null".

Parameters:

dstOffset - the offset in this sequence.

s - the sequence to be inserted.

start - the starting index of the subsequence to be inserted.

end - the end index of the subsequence to be inserted.

Returns:

a reference to this object.

Throws:

IndexOutOfBoundsException - if dstOffset
is negative or greater than this.length(), or
start or end are negative, or
start is greater than end or
end is greater than s.length()

Since:

1.5

insert

Inserts the string representation of the boolean
argument into this sequence.

The overall effect is exactly as if the second argument were
converted to a string by the method String.valueOf(boolean),
and the characters of that string were then
inserted into this character
sequence at the indicated offset.

The offset argument must be greater than or equal to
0, and less than or equal to the length
of this sequence.

insert

Inserts the string representation of the char
argument into this sequence.

The overall effect is exactly as if the second argument were
converted to a string by the method String.valueOf(char),
and the character in that string were then
inserted into this character
sequence at the indicated offset.

The offset argument must be greater than or equal to
0, and less than or equal to the length
of this sequence.

insert

Inserts the string representation of the second int
argument into this sequence.

The overall effect is exactly as if the second argument were
converted to a string by the method String.valueOf(int),
and the characters of that string were then
inserted into this character
sequence at the indicated offset.

The offset argument must be greater than or equal to
0, and less than or equal to the length
of this sequence.

insert

Inserts the string representation of the long
argument into this sequence.

The overall effect is exactly as if the second argument were
converted to a string by the method String.valueOf(long),
and the characters of that string were then
inserted into this character
sequence at the indicated offset.

The offset argument must be greater than or equal to
0, and less than or equal to the length
of this sequence.

insert

Inserts the string representation of the float
argument into this sequence.

The overall effect is exactly as if the second argument were
converted to a string by the method String.valueOf(float),
and the characters of that string were then
inserted into this character
sequence at the indicated offset.

The offset argument must be greater than or equal to
0, and less than or equal to the length
of this sequence.

insert

Inserts the string representation of the double
argument into this sequence.

The overall effect is exactly as if the second argument were
converted to a string by the method String.valueOf(double),
and the characters of that string were then
inserted into this character
sequence at the indicated offset.

The offset argument must be greater than or equal to
0, and less than or equal to the length
of this sequence.

lastIndexOf

Returns the index within this string of the rightmost occurrence
of the specified substring. The rightmost empty string "" is
considered to occur at the index value this.length().
The returned index is the largest value k such that

this.toString().startsWith(str, k)

is true.

Parameters:

str - the substring to search for.

Returns:

if the string argument occurs one or more times as a substring
within this object, then the index of the first character of
the last such substring is returned. If it does not occur as
a substring, -1 is returned.

reverse

Causes this character sequence to be replaced by the reverse of
the sequence. If there are any surrogate pairs included in the
sequence, these are treated as single characters for the
reverse operation. Thus, the order of the high-low surrogates
is never reversed.
Let n be the character length of this character sequence
(not the length in char values) just prior to
execution of the reverse method. Then the
character at index k in the new character sequence is
equal to the character at index n-k-1 in the old
character sequence.

Note that the reverse operation may result in producing
surrogate pairs that were unpaired low-surrogates and
high-surrogates before the operation. For example, reversing
"\uDC00\uD800" produces "\uD800\uDC00" which is
a valid surrogate pair.

Returns:

a reference to this object.

Since:

JDK1.0.2

toString

Returns a string representing the data in this sequence.
A new String object is allocated and initialized to
contain the character sequence currently represented by this
object. This String is then returned. Subsequent
changes to this sequence do not affect the contents of the
String.